A starter unit for an engine comprising a gear shifting clutch fitted to a main shaft of a transmission, and a one-way starter clutch interposed between a clutch gear rotating together with an input member of the gear shifting clutch and a free-wheel gear rotating around an axis of a main shaft in response to power transmission from a starter motor, are well known. For example, refer to Japanese Patent No. 2002-54540.
On the other hand, a starter unit that inputs starting operation force in response to a kick operation to a main shaft is also known, for example from Japanese Patent No. 2002-122290, and it is also possible to start an engine with a kick operation in addition to starting the engine using a starter motor.
However, with a structure where the one-way starter clutch is arranged coaxially with the main shaft, as described above, a power transmission load imposed by the one-way starter clutch is comparatively large, and with the one-way starter clutch being made large in size, there is a possibility of encouraging increase in size of the engine.
Also, in the case where it is also possible to start an engine using a kick operation, if the one-way starter clutch is arranged coaxially with the main shaft, a space for the kick start gear train to engage with the main shaft side must be ensured at a position lined up in a direction coaxial with the one-way starter clutch, making the engine extremely large in size.
The present invention has been conceived in view of the above described situation, and an object of the invention is to provide a an engine starter unit that reduces the load on a one-way starter clutch as well as effectively ensuring a space for arranging a kick start gear train, and that is capable of making an engine small in size.